High power and high energy excimer lasers have been developed for various potential directed energy applications and for laser fusion. Depending on the application, high peak power, high average power or high pulse energy are required. Rare gas halide lasers pumped by electron beam or discharge and operating in the UV produce the highest output power and pulse energy. Raman beam combining in an excimer laser-pumped Raman amplifier has been used to produce very high beam quality and has made it possible to develop 'Raman Lookthrough' techniques. Properties of various excimer laser devices developed in the U.S. will be discussed from an historical point of view.

Because short wavelength lasers are attractive for inertial confinement fusion (ICF) , the Department of Energy is sponsoring work at Los Alamos and the Naval Research Laboratory in KrF laser technology. The Los Alamos National Laboratory is investigating the feasibility of high-power KrF lasers as future ICF drivers. The Aurora Laser System is an end-to-end technology demonstration prototype for large-scale KrF laser systems employing optical angular multiplexing and serial amplification by electron beam driven KrF laser amplifiers. During the last year integration of the Aurora Laser System has been completed and the system has entered the initial operational phase by delivering kilojoule level shots to target. In this paper the current configuration of the system is described and its performance is reported.

A 5 microsec e-beam pumped XeF laser is described. Low concentrations of xenon and fluorine donor (NF3 or F2) were required to reduce losses for long-pulse operation at low (27 kW/cc) pump rates. Better performance was obtained using NF3 as the fluorine donor. The intrinsic efficiency was found to be flat over the laser pulse length, and averaged 1.1 percent. The laser output consisted of only the 353 nm line. A Rigrod treatment yielded a net gain 0.5 percent/cm.

Active-locking of 1 to 2 microsec KrF and XeF e-beam pumped oscillators has been demonstrated. Fundamental and harmonic mode-locking were performed. Individual pulse widths were approximately 1 ns full width at half maximum (FWHM). The pulses were much wider than the theoretical limit. This was caused by mechanical instability, and the difficulties of reproducing an exact cavity length of a large, single shot device. Under certain conditions, the changing index of refraction of the laser medium led to further pulse lengthening.

The amount of fluorine consumed during e-beam excitation of KrF laser mixtures is measured under lasing and nonlasing conditions. At a specific energy loading of approximately 145 J/l for a mixture of Ar/Kr/F2 = 859/142/2.8 Torr, an F2 loss of approximately 80% under lasing conditions is observed. During nonlasing conditions the loss is approximately 60%. This difference in the amount of F2 consumption between lasing and nonlasing conditions is unexpected. Additional work is suggested to verify that this is a true effect.

The performance of the XeF(C->A) laser, pumped at a rate of 290 kW/cm3 with a 600ns electron beam pulse, has been improved through the optimization of the laser gas mixture and resonator output coupler reflectivity, and by injecting radiation into the cavity from an external source so as to reduce the flux buildup time. An intrinsic efficiency of 1.8% and a specific output energy of 3 3/1 have been demonstrated, and a total output energy of 4 J has been recorded. This represents the best performance obtained thus far for any directly electrically-excited Xef(C->A) laser. The laser pulse duration was 500 ns (FWHM). The laser bandwidth has been reduced to less than 1.3 angstroms (the resolution of the spectrometer) by injecting a narrowband signal, and the wavelength of the laser has been tuned from 478.6 to 486.8 nm. The small-signal net gain has been measured during the electron beam pulse at various wavelengths, and the sidelight fluorescence spectrum has been recorded.

The performance of a scaled, repetitively pulsed injection controlled XeF (C-A) laser system is reported. A 1 Hz electron beam pumped XeF (C-A) laser system produced 0.8 J per pulse with an intrinsic efficiency of 1.5 percent. Details of a compact halogen compatible flow loop is reported. Various unstable resonator geometries were evaluated. A minimum beam divergence of 150 microrad (full angle) corresponding to a three times diffraction-limited beam was determined from far field measurements.

A derivative of the linear tri-cyclic aromatic dye, acridine, was applied to the saturable absorber for KrF lasers. Acridine in ethanol showed the best bleaching properties such as the high cross section ratio Γ =7.1 and the low saturation fluence of 1.1 mJ/cm² due to the large absorption cross section of 5.6 x 10¹⁶ cm² at 248 nm. Absorption recovery had two time constants of 0.4 ns and 115 ns. Effective filtering of ASE made it possible to control the prepulse during the ultra short pulse amplification. Picosecond pulses with sharp front edge were compressed 10 ps to 420 fs in the saturated gain KrF amplifier. Sub-picosecond pulses with high contrast ratio to ASE were generated in the high gain operation of KrF lasers.

A physical model of time, temperature, composition, and wavelength-dependent optical absorption behavior of e-beam pumped Ne/Xe/NF3(F2) plasmas is developed and discussed. A data correlation based on the progressive analysis of results pertaining to increasingly complex mixtures is developed. Comparisons of the derived model with medium absorption data are presented and discussed. Where useful, data relating to fluorescence efficiency and medium gain are used to further develop aspects of the model left obscure by the available data relating to medium absorption.

An experimental study is reported of the generation and behavior of discharge-induced shocks and waves in a compact high repetition rate XeCl excimer laser (CHIRP) with helium as buffer gas. Three sources of shocks and waves are identified. Longitudinal shocks are formed at the discharge boundaries, traveling up and downstream into the gas flow duct. A transverse shock is created at the cathode sheath region, and the anode mesh is the source of an expansion wave followed by a compression wave 1.5 microsec later. Transverse shocks can reflect off the cathode, but no reflections off the anode mesh have been observed.

Design considerations concerning a high power XeCl excimer laser are described. The subsystems to be investigated are the gas flow circulating system with a homogeneous velocity profile and thin boundary layers near the electrodes, a pulse power circuit scheme that takes care of an efficient stable discharge and the X-ray preionization source with a high repetition rate electron beam cathode. Pulse compression technology at high repetion rate plays a key role in the laser performance.

A historical overview over the development of excimer lasers into the multi-100 Watt range is given. Special emphasis is on efforts in Japan and Europe concerning excimer lasers with an average power exceeding 1 kilowatt. The overview includes a discussion of the different excitation mechanisms.

Ab initio calculations for the electronic states of (RbF)(+) ionic excimer arising from the Rb(+) + F,Rb(2+) + F(-),Rb(+) + F(-), and Rb + F(+) separated states are reported. The emission at 130 nm is identified to the transition between the ionic 2 2 Sigma(+) and l 2 Sigma(+) states which was estimated to occur at 124 nm with an spontaneous lifetime of 0.9 ns. The ionic 2 2 Pi state is found to lie close to the ionic 2 2 Sigma(+) state of a lifetime of 5.6 ns.

XeF(B) has been observed in the reaction of SiH₄ + ₂ + XeF₂. dependence of XeF(B) emission intensity on [XeF₂], [F₂], [SiH₄] and [Ar] has been measured. Possible mechanisims of XeF(B) production is discussed.

Building of high average output power excimer lasers requires the solution of several complex problems. The main challenge is the creation of a uniform discharge which can be easily reproduced even at high pulse repetition rates. Some approaches to solving this problem are discussed. They resulted in creation of lasers with aperture of 4 sq cm operating at 1 kHz producing the output of 420 W at 308 nm. A large-aperture XeCl laser can produce 10 J per pulse at 50 Hz.

Examples are given for the application o f high power excimer lasers in spectroscopy and processing of biological material. An excimer-laser pumped dye laser serves as light source for a pulsed UV Raman spectrometer which allows resonant Raman studies on nucleic acids. Experiments on the pH induced double helix formation of poly adenylic acid are described. By combining the excimer laser with a distributed feedback dye laser and a streak camera, a picosecond UV fluorescence spectrometer is built up .Tyrosine fluorescence lifetimes of selected tryptophan free peptides with up to 9 amino acids can be explained in a surprisingly simple way: only the directly neighbouring amino acid on the C-terminal side and only a few amino acids on the N-terminal side have an influence on the fluorecscence lifetime of these peptides. Besides spectroscopic applications, the excimer laser serves as light source for processing of biological material. For medical applications , high power UV Laser light has to be transmitted through light guides. A tapered light guide transmitting more than GW/cm2 is described. Microprocessing of biological material with accuracies of a few hundred nanometers can be performed when an excimer pumped dye laser is coupled into a microscope .The resulting UV laser microbeam can be used to introduce foreign genetic material into plant cells, tissues and subcellular organelles such as mitochondria and chioroplasts. Selected pairs of different cells can be fused in the UV laser microbeam under total microscopic control. Finally, one can microdissect human chromosomes and isolate DNA probes for the analysis of human disease.

The possibility to induce ablative decomposition with minimal thermal damage on organic tissues by excimer laser suggested promising medical applications of this class of lasers. Excimer laser angioplasty, which represents one of the most advanced surgical laser technique, is at present pursued by some groups at a clinical level. Original research programs in urology and dentistry, developed by our group, are also presented.

In the field of material processing excimer lasers are well suited for removal processes of polymeric materials using photochemical ablation mechanism; Pulse characteristics in combination with short wavelengths of this laser type enable high quality processing for micromachining of various metals as well. Therefore excimer lasers can become a competitor to other micromachning techniques (e.g. wet etching or galvanoforming). The removal process at metals itself is distinctly determined by process parameters as intensity, pulse quantity, pulse duration and geometrical shape/size (wavelength influences are not important), where in general only intensity and pulse quantity are controllable. Despite this, pulse duration and geometrical aspects have an essential influence on the process and should be regarded to achieve the aimed process quality. The object of this paper is to work out the removal process of metals with excimer laser radiation, concerning the influence of pulse duration and geometrical aspects described above. Nevertheless the application is limited technologically and economically to a material thickness of much less than one millimeter, since removal rates per pulse are given in the range of one to a fraction of a micron. This paper shows the capability of excimer lasers for applications in the field of drilling and cutting.

Laser processing methods have been widely used in microelectronics technology due to the following advantages: the zone of laser action can be decreased by focusing the beam into a small spot non-contact treatment eliminates undesirable introduction of impurities into laser-affected zone; the control of the energetic parameters and the spatial position of the treatment zone is relatively simple; laser treatment process is compatible with automatic control based on microprocessor systems. In this connection, the problem of laser radiation-substance interaction arises as well as the need for developing the technological processes ensuring high efficiency and quality of production, improvement of very large-scale integration (VLSI) parameters, and making products with unique characteristics.

A review of investigations of basic physical processes in gas discharge metal vapor lasers, operating on transitions from resonance to metastable level is presented. Processes during excitation pulse and also during interpulse period of time between successive excitation pulses are discussed.

We report the observation of collisional excitation energy transfer between the two upper levels of the copper vapor laser pumped by transverse discharge. When one of the two lasers (510.6 and 587.2 nm) is fed back into the laser cavity, the other laser is significantly enhanced. This opens up the new possibility of efficiently extracting the laser energy at one wavelength. This paper reports the preliminary results of the experiment.

Switching losses for resonant pulse compressors have been measured for sub-microsecond magnetisation times, for ferrite and amorphous metal alloy materials. The data provides design information for all-solid-state pulsers for operation at kilohertz rates with copper vapor lasers.

A 5 kpps copper vapor laser (CVL) switched by semiconductors has been demonstrated for the first time. The solid state power exciter consists of static induction (SI) thyristors and two stage magnetic pulse compression circuits with saturable inductors. The maximum electric efficiency was 67%. The exciter showed the high transfer efficiency in the input energy range of 2.9kW to 6.5kW by optimizing the reset currents for saturable inductors. The average laser power was 21W at a 5kpps repetition rate. An overall system jitter for synchronization was successfully reached down to a very small value of +/- 2.5ns.

Output characteristics of an externally-heated barium laser are presented. Factors affecting the average-power scaling of barium lasers have been identified through burst-mode studies, the results of which are pertinent to the design of practical, high-repetition-rate devices. Excitation processes relating to particular laser transitions are discussed.

A high-power gold vapor laser emitting 20 watts at the 627.8 nm line for an input power of 15.7 kW is described. The laser head can withstand a temperature of 1730 C. Fee expansion or shrinkage of the internal laser tube is allowed in order to prevent mechanical stress on the laser tube. The electrical circuit is a capacitor transfer circuit with a magnetic assist and a two-stage magnetic compressor. The magnetic assist prevents inverse currents in the thyratron, decreasing the harmful power consumption in the thyratron. The magnetic compressor decreases the laser current rise time to 50 nsec, enabling a thyratron current rise time of 150 nsec and obtaining a prolonged thyratron lifetime.

Copper lasers have progressed to the point where they are no longer simple research tools but are now entering the industrial arena. The high average power and high efficiency of these lasers is coupled with low running costs and improved reliability making them the laser of choice for several industrial applications. The key parameters of copper lasers are discussed along with their main industrial applications.

Atomic vapor laser isotope separation (AVLIS) is regarded as the most promising method to obtain srightly enriched economical nuclear fuel for a nuclear power plant. However, achieving a high power laser seems to be the bottle neck in its industrialization. In 1985, after successful development of high power lasers, the U.S. announced that AVLIS would be used for future methods of uranium enrichment. In Japan , Laser Atomic Separation Enrichment Research Associates of Japan (LASER-J), a joint Japanese utility companies research organization, was founded in April, 1987, to push a development program for laser uranium enrichment. Based on research results obtained from Japanese National Labs, and Universities , Laser-J is now constructing an AVLIS experimental facility at Tokai-mura. It is planned to have a 1-ton swu capacity per year in 1991. Previous to the experimental facility construction , Toshiba proceeded with the preliminary testing of an isotope separation system, under contract with Laser-J. Since the copper vapor laser (CVL) and the dye laser (DL) form a good combination , which can obtain high power tunable visible lights ,it is suitable to resonate uranium atoms. The laser system was built and was successfully operated in Toshiba for two years. The system consist of three copper vapor lasers , three dye lasers and appropriate o Atomic vapor laser isotope separation (AVLIS) is regarded as the most promising method to obtain srightly enriched economical nuclear fuel for a nuclear power plant. However, achieving a high power laser seems to be the bottle neck in its industrialization. In 1985, after successful development of high power lasers, the U.S. announced that AVLIS would be used for future methods of uranium enrichment. In Japan , Laser Atomic Separation Enrichment Research Associates of Japan (LASER-J) , a joint Japanese utility companies research organization , was founded in April, 1987, to push a development program for laser uranium enrichment. Based on research results obtained from Japanese National Labs, and Universities, Laser-J is now constructing an AVLIS experimental facility at Tokai-mura. It is planned to have a 1-ton swu capacity per year in 1991. Previous to the experimental facility construction, Toshiba proceeded with the preliminary testing of an isotope separation system, under contract with Laser-J. Since the copper vapor laser (CVL) and the dye laser (DL) form a good combination, which can obtain high power tunable visible lights, it is suitable to resonate uranium atoms. The laser system was built and was successfully operated in Toshiba for two years. The system consist of three copper vapor lasers, three dye lasers and appropriate optics. With pertinent electronics, the system total out put is 3 watts at 5 kHz repetition rate. For each CVL-DL laser set, the CVL output power was designed and operated at 20 watts and fed into DL to obtain 1 watt output. The CVL-DL sets provide three different wave lengths. Accurate wave mixing and laser pulse timing are also required during the experiment. Those laser systems, designed and manufactured in Toshiba, satisfactorily maintained a total operation time of 2000 hours during the past two years. Design work and operating experience for this laser system are described in this paper.

This paper discusses the design and performance of CuBr lasers. It is demonstrated that a sealed off CuBr laser tube of 1000 h operation is allready realizable. Investigation of the output parameters in laser tubes with a limited discharge zone shows that the output power and efficiency increase 2 times when a small amount of hydrogen is added to the neon buffer gas. We obtained from a typical CuBr laser tube with an electrode spacing of 50 cm and an i.d. of 2 cm an average output power as high as 20 W with a plug-in HV efficiency of 1.5%. At a repetition frequency of 16 kHz this implies 8 mJ/l laser energy extraction from unit active volume or 0.13 W/cm³.

Guided propagation in silica optical fibers can overcome the relatively low emission power of a copper vapor laser to produce frequency conversion by stimulated Raman scattering. Multiple Stokes generation induced by laser radiation in the fused silica of optical fibers were obtained. Conversion efficiencies up to 75 % and pulse shortening of the Stokes waves were recorded.

It has been recognized that since the He-CdII lasers are usually operated under considerably high buffer-gas pressure, the oscillation modes in these lasers can automatically reduced by their homogeneous broadening mechanism due to the high buffer-gas pressure. Therefore, it has been expected that the oscillation scheme in these lasers can easily be single-moded when they are operated in high power. We have examined this fact with a most high-power (100mW) He-CdII white light laser which has just come to be commercially available in Japan. As a result, this is true only in the cases of the 537.8 nm and 636.Onm lines, but in the case of the 441.6nm lines an anomalous broadening of the spectral width, which amounts to as much as more than 2GHz has been measured. This degrades the coherence length of this blue line less than 15cm. Such a large broadening can be attributed to the isotopes involved in the natural cadmium metal used for the laser material.

The laser material processing is now very popular in the modern industry, and the market of the laser machine for material processing exceeded 80 billion yen in 1988 with 35% increase in the recent 10 years in Japan. All of lasers used for those machines in the industry are CO2 or YAG lasers, because these two lasers are stable, reliable, and of good characteristics with reasonable costs. However, many people consider those two lasers are not so good enough and the future laser for processing should be much better in many aspects. The question is whether or not the future laser is still CO2 and YAG?

Recent progress in development of tunable midinfrared gas lasers and their application at Riken is reviewed. Emphasis is placed on the development of a high average power TEA CO2 laser with an all-solid-state exciter, which will be used as a pump source of a para-H2 rotational Raman laser. A 1-kHz operation of the TEA CO2 laser and its scaling to vary high power are described. Widely-tunable wavelength conversion of TEA CO2 laser based on stimulated rotational Raman scattering is also discussed.

We have developed a comprehensive theoretical model dealing with both variations of laser output energy and laser gas composition as a function of the repetitive laser pulse in order to evaluate the performance characteristics of the high-power, closed-cycle transversely excited (TE) CO₂ laser. According to our analysis, the number of CO₂ molecules decomposed per unit input energy of single discharge pulse was calculated to be 1.45x10¹⁷ molecules/J for the laser gas mixture of C0₂/N₂/He=l5/l5/70. The number of N₂ molecules decomposed per unit input energy density was calculated to be about 24000 times smaller than that of CO₂. Our model theoretically predicted for the first time that a very little quantity of water vapor (<50 ppm) in the laser gas dramatically decreased the equilibrium CO₂ decomposition level, resulting in increasing the laser output energy.

A new technique to excite a CO₂ laser by 2.45GHz microwave discharge is developed. Microwave plasma produced by the technique is so stable and homogeneous that any additional means to effectuate laser action such as fast circulation of laser gas and external magnetic field are not necessary. Utilizing the technique, a compact diffusion cooled CO₂ laser with 40cm active length is constructed. A magnetron available for microwave ovens is used as the power source of the laser. Average output power of 116W and maximum conversion efficiency of 18% in CW mode, peak output power of 1.2kW in pulse mode are obtained. Output beam with good focusibility is extracted by applying an unstable-waveguide hybrid resonator.

Ignition voltages and pulsed and CW vector impedance measurements have been made for a fast axial flow RF excited CO₂ laser, enabling quantitative design work on the RF power system. Comparisons are made between laser power control by analogue RF power and pulse modulation.

A high power CO₂ laser equipped with an unstable resonator with a phase-unifying output coupler has been developed to produce highly focusing beam. A linear polarized, diffraction-limited beam of 5kW with divergence angle of 0.6 mrad has been extracted stably from a laser excited by a high-frequency silent discharge.

The results of experimental and theoretical investigations of the different methods of phase locking of an array of lasers, the selection one supermode and the increasing of energy in mane maximum of focal spot are described. The practical realization of this methods opens the real perspectives to improve the brightness of radiation of multibeain CO₂ lasers and to expand the area of there application in the thermal technology.

Some of the electrical characteristics of a powerful TEA CO₂ laser with plasma electrodes are investigated experimentally. Moreover, a simplified numerical modeling of the laser electrical characteristics is performed. The calculations show a good agreement with the experimental results. The homogeneity of the laser medium is experimentally investigated too.

Investigations of currents in close-to surface plasma, produced by CO₂- laser radiation of different temporal structure have been carried out. The character of evolution of registered currents temporal structure at growing energy density was different when the target was irradiated in air and in vacuum by the train of short (τ= 2.5 ns ) pulses. Experiments in vacuum have revealed that the transit from smooth single mode pulse to the nanosecond pulse train of the same total energy was followed by a considerable decrease in plasma formation energy thresholds and by the increase of amplitudes of currents induced by plasma. The current pulses from the target were registered after finishing the laser irradiation; their appearance was probably connected with cumulation effects, caused by the ring form of the irradiated area.

The latest results on studying EBCD lasers on CO2, CO, N2O molecular gases carried out at the Gas Lasers Lab of Lebedev Institute are reported. EBCD CO2 isotope lasers, cryogenic and supersonic-cooled, pulsed and pulse repetition CO lasers and amplifiers, and high efficiency N2O lasers have been investigated. A high-power N2O laser has been created with energy, specific output, and efficiency of 106 J, 36 J/l-Amagat, and 10 percent, respectively.

The present status of the chemical oxygen-iodine laser is discussed. The pertinent processes occurring in the chemical O2 generator, the O2(1Delta) transport region, and the nozzle are reviewed. The energy transfer kinetics, laser gain, and the performance and device efficiency are examined.

A simple model for predicting the small signal gain as a function of flow direction will be presented. The small signal gain was measured on the Weapons Laboratory Rotocoil 0₂/I^* gain medium. The characteristics observed in the experiment show a decrease in the small signal gain as a function of distance from the nozzle exit plane. Further results indicated that the small signal gain decreased with time and that the gain increased when the cold trap was turned on. All of these effects suggest a temperature dependence of the small signal gain. The approach presented in this paper is to develop a simple model which includes a simplified kinetics model and the gas dynamics for the flowing medium. An analytic solution to the model equations is also derived. These models account for the reduction in small signal gain in the flow direction due to heat release into the cavity when compared to the Rotocoil small signal gain data. The results show that the rise in gas temperature in the flowing 0₂/I^* medium is primarily due to water deactivation of the I^* and the O₂(1Δ) plus I^* pooling leading to water deactivation of ¹Σ. Such temperature rise in the flowing medium causes the small signal gain to decay substantially in the flow direction due to the square root of the temperature dependence in the stimulated emission cross section, the shift in the equilibrium constant with temperature and the decrease in density which is inversely proportional to the temperature.

We have developed a kW-class chemical oxygen iodine laser with industrial applications in mind. The laser system shows stable and efficient operation. Using the present system we have demonstrated optical power transmission through a silica fiber with very high transmission efficiency.

A time-dependent model of a single-pass amplifier which treats upper laser level pumping by O2(1 Delta), deactivation by water, and stimulated emission within the flowing oxygen-iodine medium is described. An efficient algorithm for solving the coupled, flowing medium, and optical extraction equations is presented. The model indicates that extraction efficiencies comparable to CW efficiencies can be obtained with pulse repetition rates comparable to the rate of flow through the cavity and pulse lengths of the order of the time it takes to extract the energy stored in O2(1 Delta).

The Zeeman effect is used here to demonstrate a gas-phase, self-healing Q-switch for a kwatt-class chemical oxygen-iodine laser. Enhancement ratios of pulse power over CW power of 16 to 1 are achieved with extraction efficiencies of 75 percent. The flows of each type of chemical are presented, and the laser configurations are shown.

A flow reactor using the 2F + HN₃ reaction to generate NF(a¹Δ) has been used to systematically study the reactions of NF(a¹Δ) at 300K. The biomolecular self-removal rate constant for NF(a¹Δ) was assigned as 5 +/- 2 x 10^-12 cm³s^-1 . Quenching rate constants by stable molecules span a wide range of values; those for diatomic molecules, with the notable exception of the halogens, generally are less than 1 x 10^-14 cm³s^-1 , but more reactive molecules, such as C₂H₄, NH₃ and P(CH₃)₃, have rate constants of l x 10^-11 cm³s^-1 . For those polyatomic molecules which can act as Lewis bases, a correlation exists between the magnitude of the quenching rate constant and the base strength. The rate constants for the halogens increase dramatically with molecular weight and the rate constant for I₂ is (1.5+/-1.0) x 10^-10 cm³s^-1 . The rate constants for open shell atoms and molecules tend to be smaller than expected; values for NO₂, N0, F, N, 0 and C are 0.65 x l0^-14 , 0.10 x 10^-14, 4 x 10^-13 , 5 x 10^-13 , 6 x 10^-12 and 2.7 x 10^-11 cm³s^-1, respectively. In general, the NF(a¹Δ) quenching rate constants are not so large as to preclue the utilization of complex schemes to extract the stored energy of NF(a¹Δ).

Three chemical systems have been proposed for generating a visible electronic transition laser on NF(b - X) at lambda = 529 nm. Each concept involves generating NF(a 1 Delta) and upconverting it to NF(b 1 Sigma). The stimulated emission cross section for NF(b - X) is small due to a small Einstein coefficient and rovibronic dilution of the oscillator strength. Large inversion densities are mandated which raise problems with gas phase side reactions involving the collision of two excited state species. In addition, the combination of low gain and high energy storage density results in large intracavity fluxes for a real laser device.

A visible chemical laser on the BiF(A-X) transistions at 430-470 nm can potentially be generated by the interaction of Bi-atoms with metastable species such as NF(a¹Δ). Experiments were performed in which these constituents were obtained in situ by fast pulsed CO₂ laser pyrolysis of FN₃ and Bi(CH₃)₃, respectively. Time-resolved optical diagnostics were used to follow the concentrations of FN₃, NF(a¹Δ), Bi(CH₃)_x, Bi(²D) and BiF(A). The optimal concentrations of FN₃ and Bi(CH₃)₃ were limited by NF(a¹Δ) self-annihilation and Bi(²D) quenching reactions, respectively. The Bi(CH₃)₃ was found to be only 20 % dissociated at the peak of the NF(a¹Δ) time profile and the yield of Bi-atoms from dissociated Bi(CH₃)₃ was determined to be approximately 5%; however, significant recycling of the active Bi/BiF species was observed at a limiting rate of 4 - 5 x 10-11 cm³/s, driven by NA(a¹Δ). On the basis of these results, a peak BiF(A) concentration of 10¹³/cm³ was predicted by kinetic modeling and subsequently observed. The model also predicts an absolute population inversion of the BiF(A-X) transistion at high NF(a¹Δ) concentration with unsaturated gains of approximately 10^-3/cm. Intracavity experiments have verified that the BiF(X) ground state concentration is low enough relative to the excited state to generate at least a partial inversion, and initial evidence for an absolute population inversion has been obtained.

A series of experiments was conducted in which trimethylbismuthine (TMB) was used to introduce atomic bismuth into a supersonic flow of electronically excited nitrogen fluoride, NF(a¹Δ), at an elevated density of 3 x 10¹⁵ mol cm^-3. Excited-state densities of Bi(²D) approximately equal to 1 x 10¹³ atom cm^-3 and BiF(AO⁺) approximately equal to 4 x 1O¹¹ mol cm^-3 were achieved. After correction for mixing, these density values agreed reasonably well with values predicted by a quadratic scaling law. Simulation of the blue BiF(AO⁺)-BiF(XO⁺) emission spectrum suggests that the BiF(AO⁺) was in vibrational as well as rotational equilibrium at 300°C. The significance of these results for developing a supersonic BiF(AO⁺) laser utilizing TMB is discussed.

Fluid dynamic and chemical mechanisms are coupled to define a flow configuration tailored to the requirements of proposed short-wavelength chemical lasers operating on NF(b-X) transitions. A novel blowdown combustion facilty approach to the experimental study of advanced chemical laser and other fluid dynamic phenomena is defined and its adaptation to the study of NF laser mechanisms is described in detail. The facility design allows the generation of high gain-length test flows and the variation of combined fluid dynamic and chemical properties over wide ranges of operation in a laboratory environment. Results from initial studies in the facility are described.

Directed energy weapons can add significantly to the effectiveness of a Strategic Defense System (SDS) by complementing the capabilty of phase I kinetic energy weapons. Component development for each of the directed energy concepts is progressing well. The chemical laser and neutral particle beam programs are nearing the stage where component integration tests are essential for establishing engineering proof-of-principle. For the somewhat less mature ground-based free electron laser technology, device development will be emphasized during the next several years. Development of the acquisition, tracking and pointing (ATP) program will continue at a fast pace, with an exciting proof-of-principle test to occur in space in early 1990. The directed energy program remains on track to provide information to support a national decision on strategic defense in the 1991/1993 timeframe.

The performance of a cw HF chemical laser master oscillator with power amplifier was measured as a function of input power, oscillator/amplifier flow field match/mismatch and location of the optical axis of the input beam. The amplification ratio is an inverse function of the input power (intensity) and, for maximum amplification, the peak of the intensity distribution must be matched to the peak of the zero power gain distribution in the amplifier. The match/mismatch of the oscillator/amplifier flow fields has a second order effect on amplifier performance. The measured P_out versus P_in performance curve showed that, after a continuous increase, the difference P_out-P_in remained almost constant over a wide range of input powers and that about one third of a device's oscillator output must be input to obtain amplifier output equal to the device's oscillator performance. When the input beam contained time-dependent oscillations, the amplitude modulation of the output beam was reduced by a factor that equaled the amplification ratio of the amplifier; the amplifier had no effect on the period (frequency) of the oscillations of the input beam. An amplifier performance model that predicts a device's amplifier performance given the device's oscillator performance as a function of reflectivity was developed. Excellent agreement between model predictions and experimental data was obtained. The model was used to predict multiple pass amplifier performance. The results showed that, with a two pass amplifier, one oscillator could drive six amplifiers. When the amplifier performance curves were plotted in terms of ζ_out versus ζ_in, where ζ=P_AMP/P_OSC, the curves for different devices collapse to one.

It is proposed that the diffraction theory of aberration be used to evaluate approximately the optimal focused area of a high-power laser and the intensity distribution at the focused area. In one proposed method, the phase distribution of the laser beam is yielded by processing the interference fringe obtained from the front of the focal lens of the laser system. The amplitude distribution can either be assumed as super-Gaussian in shape with low frequency modulation, or can be simulated by computing the laser propagation using an FFT algorithm with real samples. In another method, the irradiation distributions are demonstrated experimentally using hologram reconstruction. This method can provide more details of the focused laser beam than digital computation.

In order to improve the transmission efficiency of laser beam having larger beam diameter and divergence into an optical fiber, We have deduced criteria for choosing optimal focal length of a single lens coupling system in this paper. By which the minimum size of focal spot could be obtained. These criteria were used in design of a lens-optical fiber delivery system. From which more than 70% efficiency has been reached for a gold vapor laser having φ40mm beam diameter.

Temporal, spatial and energy characteristics of copper vapor laser with confocal unstable and self-filtering unstable resonators are presented. Conditions for obtaining diffraction-limited divergence of radiation were founded experimentally when light passed only one round-tripp for different magnifications of resonator, diameters of active medium and field-limiting aperture. Comparison is carried out for output characteristics of oscillator-amplifier system with different types of oscillator resonator. Application of this system to laser precise machining is mentioned.

Emission from I(²P_1/2) at 1.315 micron has been observed from the energy transfer from NCl(a¹Δ) to I(²P_3/2). The NCl(a¹Δ) was produced by reacting excess Cl with HN₃. The Cl and HN₃ react to give N₃ and HCl. The N₃ then reacts with Cl to yield NCl(a¹Δ) and N₂. A rate constant for the quenching of NCl(a¹Δ) by I(2 P 3/2) was measured to be at least 1 x 10^-10 cm³/s. This near gas kinetic rate is interpreted as evidence of an efficient near resonance energy transfer process; NCl(a¹Δ, v = 0) + I(²P_3/2) - NCl(X³Σ, v = 2) + I(²P_1/2).

A high-pressure pulsed chemical singlet oxygen generator is developed. Obtained maximum singlet oxygen pressure is 20 torr, and excitation efficiency in that moment is crudely estimated to be 40 percent. Experimental results are compared with numerical calculation. Two applications of this generator are presented along with brief evaluation of specifications.